#.  Copyright (C) 2005-2010   Gregory P. Smith (greg@krypto.org)
#  Licensed to PSF under a Contributor Agreement.
#

__doc__ = """hashlib module - A common interface to many hash functions.

new(name, data=b'') - returns a new hash object implementing the
                      given hash function; initializing the hash
                      using the given binary data.

Named constructor functions are also available, these are faster
than using new(name):

md5(), sha1(), sha224(), sha256(), sha384(), and sha512()

More algorithms may be available on your platform but the above are guaranteed
to exist.  See the algorithms_guaranteed and algorithms_available attributes
to find out what algorithm names can be passed to new().

NOTE: If you want the adler32 or crc32 hash functions they are available in
the zlib module.

Choose your hash function wisely.  Some have known collision weaknesses.
sha384 and sha512 will be slow on 32 bit platforms.

If the underlying implementation supports "FIPS mode", and this is enabled, it
may restrict the available hashes to only those that are compliant with FIPS
regulations.  For example, it may deny the use of MD5, on the grounds that this
is not secure for uses such as authentication, system integrity checking, or
digital signatures.   If you need to use such a hash for non-security purposes
(such as indexing into a data structure for speed), you can override the keyword
argument "usedforsecurity" from True to False to signify that your code is not
relying on the hash for security purposes, and this will allow the hash to be
usable even in FIPS mode.

Hash objects have these methods:
 - update(arg): Update the hash object with the bytes in arg. Repeated calls
                are equivalent to a single call with the concatenation of all
                the arguments.
 - digest():    Return the digest of the bytes passed to the update() method
                so far.
 - hexdigest(): Like digest() except the digest is returned as a unicode
                object of double length, containing only hexadecimal digits.
 - copy():      Return a copy (clone) of the hash object. This can be used to
                efficiently compute the digests of strings that share a common
                initial substring.

For example, to obtain the digest of the string 'Nobody inspects the
spammish repetition':

    >>> import hashlib
    >>> m = hashlib.md5()
    >>> m.update(b"Nobody inspects")
    >>> m.update(b" the spammish repetition")
    >>> m.digest()
    b'\\xbbd\\x9c\\x83\\xdd\\x1e\\xa5\\xc9\\xd9\\xde\\xc9\\xa1\\x8d\\xf0\\xff\\xe9'

More condensed:

    >>> hashlib.sha224(b"Nobody inspects the spammish repetition").hexdigest()
    'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2'

"""

# This tuple and __get_builtin_constructor() must be modified if a new
# always available algorithm is added.
__always_supported = ('md5', 'sha1', 'sha224', 'sha256', 'sha384', 'sha512')

algorithms_guaranteed = set(__always_supported)
algorithms_available = set(__always_supported)

__all__ = __always_supported + ('new', 'algorithms_guaranteed',
                                'algorithms_available', 'pbkdf2_hmac')

import functools
def __ignore_usedforsecurity(func):
    """Used for sha3_* functions. Until OpenSSL implements them, we want
    to use them from Python _sha3 module, but we want them to accept
    usedforsecurity argument too."""
    # TODO: remove this function when OpenSSL implements sha3
    @functools.wraps(func)
    def inner(*args, **kwargs):
        if 'usedforsecurity' in kwargs:
            kwargs.pop('usedforsecurity')
        return func(*args, **kwargs)
    return inner


__builtin_constructor_cache = {}

def __get_builtin_constructor(name):
    cache = __builtin_constructor_cache
    constructor = cache.get(name)
    if constructor is not None:
        return constructor
    try:
        if name in ('SHA1', 'sha1'):
            import _sha1
            cache['SHA1'] = cache['sha1'] = _sha1.sha1
        elif name in ('MD5', 'md5'):
            import _md5
            cache['MD5'] = cache['md5'] = _md5.md5
        elif name in ('SHA256', 'sha256', 'SHA224', 'sha224'):
            import _sha256
            cache['SHA224'] = cache['sha224'] = _sha256.sha224
            cache['SHA256'] = cache['sha256'] = _sha256.sha256
        elif name in ('SHA512', 'sha512', 'SHA384', 'sha384'):
            import _sha512
            cache['SHA384'] = cache['sha384'] = _sha512.sha384
            cache['SHA512'] = cache['sha512'] = _sha512.sha512
    except ImportError:
        pass  # no extension module, this hash is unsupported.

    constructor = cache.get(name)
    if constructor is not None:
        return constructor

    raise ValueError('unsupported hash type ' + name)


def __get_openssl_constructor(name):
    try:
        f = getattr(_hashlib, 'openssl_' + name)
        # Allow the C module to raise ValueError.  The function will be
        # defined but the hash not actually available thanks to OpenSSL.
        # We pass "usedforsecurity=False" to disable FIPS-based restrictions:
        # at this stage we're merely seeing if the function is callable,
        # rather than using it for actual work.
        f(usedforsecurity=False)
        # Use the C function directly (very fast)
        return f
    except (AttributeError, ValueError):
        # TODO: We want to just raise here when OpenSSL implements sha3
        # because we want to make sure that Fedora uses everything from OpenSSL
        return __get_builtin_constructor(name)


def __py_new(name, data=b'', usedforsecurity=True):
    """new(name, data=b'', usedforsecurity=True) - Return a new hashing object using
    the named algorithm; optionally initialized with data (which must be bytes).
    The 'usedforsecurity' keyword argument does nothing, and is for compatibilty
    with the OpenSSL implementation
    """
    return __get_builtin_constructor(name)(data)


def __hash_new(name, data=b'', usedforsecurity=True):
    """new(name, data=b'', usedforsecurity=True) - Return a new hashing object using
    the named algorithm; optionally initialized with data (which must be bytes).
    
    Override 'usedforsecurity' to False when using for non-security purposes in
    a FIPS environment
    """
    try:
        return _hashlib.new(name, data, usedforsecurity)
    except ValueError:
        # TODO: We want to just raise here when OpenSSL implements sha3
        # because we want to make sure that Fedora uses everything from OpenSSL
        return __get_builtin_constructor(name)(data)

try:
    import _hashlib
    new = __hash_new
    __get_hash = __get_openssl_constructor
    algorithms_available = algorithms_available.union(
            _hashlib.openssl_md_meth_names)
except ImportError:
    new = __py_new
    __get_hash = __get_builtin_constructor

try:
    # OpenSSL's PKCS5_PBKDF2_HMAC requires OpenSSL 1.0+ with HMAC and SHA
    from _hashlib import pbkdf2_hmac
except ImportError:
    _trans_5C = bytes((x ^ 0x5C) for x in range(256))
    _trans_36 = bytes((x ^ 0x36) for x in range(256))

    def pbkdf2_hmac(hash_name, password, salt, iterations, dklen=None):
        """Password based key derivation function 2 (PKCS #5 v2.0)

        This Python implementations based on the hmac module about as fast
        as OpenSSL's PKCS5_PBKDF2_HMAC for short passwords and much faster
        for long passwords.
        """
        if not isinstance(hash_name, str):
            raise TypeError(hash_name)

        if not isinstance(password, (bytes, bytearray)):
            password = bytes(memoryview(password))
        if not isinstance(salt, (bytes, bytearray)):
            salt = bytes(memoryview(salt))

        # Fast inline HMAC implementation
        inner = new(hash_name)
        outer = new(hash_name)
        blocksize = getattr(inner, 'block_size', 64)
        if len(password) > blocksize:
            password = new(hash_name, password).digest()
        password = password + b'\x00' * (blocksize - len(password))
        inner.update(password.translate(_trans_36))
        outer.update(password.translate(_trans_5C))

        def prf(msg, inner=inner, outer=outer):
            # PBKDF2_HMAC uses the password as key. We can re-use the same
            # digest objects and just update copies to skip initialization.
            icpy = inner.copy()
            ocpy = outer.copy()
            icpy.update(msg)
            ocpy.update(icpy.digest())
            return ocpy.digest()

        if iterations < 1:
            raise ValueError(iterations)
        if dklen is None:
            dklen = outer.digest_size
        if dklen < 1:
            raise ValueError(dklen)

        dkey = b''
        loop = 1
        from_bytes = int.from_bytes
        while len(dkey) < dklen:
            prev = prf(salt + loop.to_bytes(4, 'big'))
            # endianess doesn't matter here as long to / from use the same
            rkey = int.from_bytes(prev, 'big')
            for i in range(iterations - 1):
                prev = prf(prev)
                # rkey = rkey ^ prev
                rkey ^= from_bytes(prev, 'big')
            loop += 1
            dkey += rkey.to_bytes(inner.digest_size, 'big')

        return dkey[:dklen]


for __func_name in __always_supported:
    # try them all, some may not work due to the OpenSSL
    # version not supporting that algorithm.
    try:
        func = __get_hash(__func_name)
        if 'sha3_' in __func_name:
            func = __ignore_usedforsecurity(func)
        globals()[__func_name] = func
    except ValueError:
        import logging
        logging.exception('code for hash %s was not found.', __func_name)

# Cleanup locals()
del __always_supported, __func_name, __get_hash
del __py_new, __hash_new, __get_openssl_constructor
del __ignore_usedforsecurity